In a storage apparatus, when a plurality of storage devises are implemented, a relaying apparatus for forwarding data transmitted from the control apparatus to each storage device is used. The storage device is a drive such as an HDD (Hard Disk Drive) and an SSD (Solid State Drive) that support an SAS (Serial Attached SCSI), for example. The control apparatus is a CM (Control Module) or the like, for example. The relaying apparatus is an expander or the like, for example.
When accessing a storage device, a host computer transmits an access request with an attached LUN (Logical Unit Number) to the control apparatus. The host computer is an information processing apparatus such as a server, for example. An access request is a request for writing of data and reading of data, for example. Then, the host computer executes writing of data into the storage device and reading of data from the storage device by transmitting an access request to the storage device. In the explanation below, the host computer may simply be referred to as a host.
The control apparatus is equipped with a memory, for example. Meanwhile, the memory stores a management table in which identifiers that identify connection units provided in the relaying apparatus are associated with and stored with the LUNs. The connection unit is a PHY (Physic Layer) or the like, for example. The PHY is a physical port in the SAS standard. The identifier is a PHY number, for example. The PHY number is the port number of the PHY.
Upon receiving an access request with an attached LUN from the host, the control apparatus performs a search in the management table, and the control apparatus extracts a first identifier associated with the LUN. Then, the control apparatus transmits the access request with the extracted first identifier attached to the access request, to the relaying apparatus.
Upon receiving the access request with the attached first identifier, the relaying apparatus forwards the access request to the storage device via a first connection unit identified by the first identifier.
According to the above, the host accesses the storage device, and the host executes writing of data into the storage device and reading of data from the storage device.
As another related technique, a technique has been known (for example, Japanese National Publication of International Patent Application No. 2009-540436) in which an SAS expander includes SAS PHYs to transmit and receive signals to and from SAS devices on corresponding SAS links connected to the SAS PHYs. The SAS expander includes a status register that provides a failure detection parameter regarding the communication on the SAS link. The microprocessor of the SAS expander identifies the communication which is having a failure in one of the SAS links, according to the failure detection parameter.
In the relaying apparatus in the relaying technique described above, when a link-down occurs between a first connection unit and a storage device, the storage device to which the link-down has occurred is connected to a second connection unit which is an extra connection unit in the relaying apparatus, and a link-up occurs to the second connection unit. At this time, there is a problem wherein higher-order apparatuses such as the host and the control apparatus identify the storage device according to the identifier that identifies the connection unit to which the storage device is connected, and therefore, it is impossible to access the storage device to which the link-down has occurred in the same manner as before the link-down.